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A(n) ________ is any sequence of letters and numbers, and is designated by quotation marks

Fill in the blank(s) with the appropriate word(s).

S1 returns the total number of credits for which Joe is registered, together with his Id. T maintains the integrity constraint “no student shall register for more than 20 credits.” If Joe has less than 20 credits, T executes S2 to increment the number of credits for which Joe has registered in a particular course. Suppose Joe executes two instances of T concurrently at the following isolation levels. In each case say whether or not the named violation of the constraint can occur and, if the answer is yes, explain how(e.g., what locks are or are not held).

A database has two tables:

Student(Id, Name, ...)—Id and Name are both unique
Registered(Id, CrsCode, Credit, ...)—contains one rowfor each course each
student is taking this semester

A transaction type, T, has two SQL statements, S1 followed by S2 (w ith local computations between them):

S 1 SELECT SUM(R.Credits), S.Id
INTO :sum, :id
FROM Student S, Registered R
WHERE S.Name = ’Joe’ AND S.Id = R.Id
GROUP BY S.Name, S.Id

S 2 UPDATE Registered
SET Credits = Credits + 1
WHERE Id = :id AND CrsCode = :crs

a. READ COMMITTED lost update b. REPEATABLE READ lost update c. SNAPSHOT lost update